The difference between a contract so sell and a conditional deed of sale is well enunciated in the case law VENTURA et. al. v. ENDAYA et. al.1, to wit:


A contract to sell is defined as a bilateral contract whereby the prospective seller, while expressly reserving the ownership of the subject property despite delivery thereof to the prospective buyer, binds himself to sell the said property exclusively to the latter upon his fulfillment of the conditions agreed upon, i.e., the full payment of the purchase price and/or compliance with the other obligations stated in the contract to sell. Given its contingent nature, the failure of the prospective buyer to make full payment and/or abide by his commitments stated in the contract to sell prevents the obligation of the prospective seller to execute the corresponding deed of sale to effect the transfer of ownership to the buyer from arising. As discussed in Sps. Serrano and Herrera v. Caguiat:


A contract to sell is akin to a conditional sale where the efficacy or obligatory force of the vendor's obligation to transfer title is subordinated to the happening of a future and uncertain event, so that if the suspensive condition does not take place, the parties would stand as if the conditional obligation had never existed. x x x.


To note, while the quality of contingency inheres in a contract to sell, the same should not be confused with a conditional contract of sale. In a contract to sell, the fulfillment of the suspensive condition will not automatically transfer ownership to the buyer although the property may have been previously delivered to him. The prospective seller still has to convey title to the prospective buyer by entering into a contract of absolute sale. On the other hand, in a conditional contract of sale, the fulfillment of the suspensive condition renders the sale absolute and the previous delivery of the property has the effect of automatically transferring the seller’s ownership or title to the property to the buyer. (Citations omitted)


 1G.R. No. 190016 , October 2, 2013.